Question
I've got two globe-shaped arborvitae, which have done well in full-partial shade garden in southwest Missouri.  This year we've had drought conditions with severe heat this summer. Although I've watered periodically, one of the shrubs is turning brown rapidly throughout the plant. It looks like it is dying.  Could it be the heat and drought? The one next to it probably gets slightly less sun, but is showing some brown areas as well.  How should I treat this?  THANKS!

Answer
Amy,
There are two possible insects that could be attacking the arbs.
The first is Arborvitae leafminer. These tiny insects eat away at the insides of the leaves, causing them to brown out. Use orthene or any systemic insecticide to stop further damage. To tell if this is the problem, take one of the brown needles and break it open- if it is hollow, then the leafminer is active.
The second insect is mites. These tiny arachnids suck the juices out of the leaves of the plant. Use a registered miticide to control these pests. To check for this pest, place a sheet of white paper under the branches and shake the branch- if you see tiny red or black specks crawling on the paper, then mites are present.
I would also recommend watering every other day for at least 45 minutes using a soaker hose. Fertilize them in the fall and again in the spring to stimulate new growth.
Good luck.
Ed Gulliksen